Chowdhury actually confirmed his exit yesterday on Twitter, but everyone seemed to miss it (hopefully because everyone was watching Disrupt). He came over to the service with the Summize acquisition in 2008. He was a co-founder of that search engine alongside Greg Pass, who left his CTO position at Twitter in May. We’re told that all of the original Summize team is now gone from Twitter. (Update: Looks like Eric Jensen and Matt Sanford are leaving today.)

As Chief Scientist, Chowdhury led a number of important data projects at Twitter over the years. He was key in implementing Twitter Search, Recommendations, and Trends. Twitter declined to comment on Chowdhury’s departure.

While Chowdhury’s departure is a big one, there’s quite a bit of talk out there of even bigger ones. This is all likely related to Twitter’s latest massive round of funding. We’re looking into it. Stay tuned.